The present invention relates to digital video systems, and more particularly, to circuits for generating picture reconstruction control or steering bits in the event of a tie for closest match to a deleted sample by surrounding samples.
In digital broadcast systems, the effective use of the data rate is of primary importance. A reduction in data rate reduces both video tape usage and the necessary transmission bandwidth; however, this must be accomplished while maintaining broadcast quality pictures.
One method of data rate reduction which is presently under consideration is the process of sub-Nyquist sampling, such as is disclosed in the paper "Sub-Nyquist Encoded PCM NTSC Color Television" by John P. Rossi in the book "Digital Video", a review of SMPTE papers, and in the article by Leonard S. Golding, "Frequency Interleaved Sampling of a Color Television Signal", IEEE Transactions on Communication Technology, Volume COM-19, page 972, December, 1971. These sub-Nyquist type systems have samples with the diagonal distance between the samples being greater than the horizontal distance between the samples. Since the smaller the distance between samples the greater the resolution, these systems are capable of increasing the horizontal resolution which is available at a given data rate, but at the expense of the diagonal resolution.
A system for overcoming this disadvantage is shown in U.S. patent application No. 132,137, filed Mar. 20, 1980, (RCA 74,547), now abandoned in favor of continuation application Ser. No. 168,077, filed July 14, 1980 (RCA 74,547A), both entitled "Data Rate Reduction For Digital Video Signals By Subsampling And Adaptive Reconstruction". The method of said applications comprises dividing a signal into first and second time portions, transmitting the first portion, and transmitting a control signal adapted to control the reconstruction of said second portion from the transmitted first portion. The control signal is generated by comparing combinations of samples of the transmitted first portions with a sample of the untransmitted second portions, and determining which combination is the closest match to the second portion sample, the control signal indicating which combination is the closest match for best reconstruction of untransmitted second portion samples at a receiver. However, a problem arises if at least two of said combinations are tied for best match. The circuitry will generate a control signal that indicates that an arbitrary one of said tied combinations is the best match. This sometimes results in "artifacts", which are black or white speckles occurring at the intersection horizontal and vertical lines or at the intersection of diagonal lines. It is therefore desired to reduce the occurrence of artifacts.